Mucin is a major component of mucus, which functions to secrete mucus to the epithelial cells of the digestive system, and respiratory organs such as the airway. Thus, it functions to protect the intestinal surface, which is epithelial tissue, from the mechanical damage and chemical stimulation of each organ and acts as a lubricant for a bowel movement. 20 mucin genes performing such functions have been identified to date and can be broadly divided, according to function, into secretory mucins (MUC2, MUC5AC, MUC5B, MUC6, MUC7, MUC9 and MUC19) and membrane-bound mucins (MUC1, MUC3A, MUC3B, MUC4, MUC12, MUC17, MUC18 and MUC20). The membrane-bound mucins are involved in the secretion and migration of the secretory mucins.
Among such mucin genes, the secretory mucins MUC2, MUC5AC, MUC5B and MUC6 genes are clustered on human chromosome 11p15.5 to form a gene cluster (FIG. 1). Also, such structural characteristics were also found in mouse genomes.
This indicates that the structural characteristics of a cluster of genes having the same function are highly conserved in other species, and the group of the secretory mucin genes is considered to have a close connection with the relative expression and function of genes.
When the secretory mucin genes are in a normal state, they will secrete mucus from different organs to protect each organ and the intestines, but when they are regulated or have abnormality, they will excessively secrete mucus. It has been reported that, in the case of bronchi, such excessive secretion causes asthma or involves inflammatory disease, and in the case of gastric cancer, excessive mucus increases tolerance to various pathogenic bacteria, thus increasing the incidence of tumors such as gastric cancer.
Also, the secretory mucins were observed to commonly have tandem repeats (TRs) in the central region of the genes. It was reported that, due to such TR structures, the mucosal characteristics of mucin appear, and structural mutations in the TR regions are attributable to genetic diseases found in human beings. These mucin genes having highly complex structural characteristics are not yet completely separated in the genome, but the base sequences thereof are gradually being identified as a result of the human genome project.
Many recent studies revealed that such tandem repeat (TR) sequences take up more than 10% of the human genome, cause many diseases and are very important factors in the regulation and evolution of gene expression. The TR sequences are divided, according to length thereof, into monomorphic sequences having only a single length in all individuals, and polymorphic sequences, which have more than 2 alleles and vary depending on individuals. The polymorphic repeat sequences have important meaning as genomic markers which can be used in human genome mapping in initial genomics studies. Thus, the analysis of TRs and polymorphisms in the structurally highly complex mucin genes allows studies on the correlation of the genes with diseases.
Meanwhile, telomerase is a ribonucleoprotein complex consisting of active subunit TERT (human telomerase reverse transcriptase) and TR (telomerase RNA) as a RNA component that provides a template for the synthesis of telomeric DNA. Telomerase is expressed mainly in germ cells and stem cells as reproductive cells of adult somatic cells, but is not expressed in other somatic cells, and thus the length of the telomere region is gradually shortened with an increase in cell division rate. When telomeres are significantly shortened, DNA damage checkpoint will be activated, cell division will be stopped, and cell aging will be induced. Thus, the activation of telomerase appears in most tumor cells where cell aging does not occur.
The RNA component of telomerase is expressed in most embryonic and adult tissues, but the expression of TERT correlates directly with the activity of telomerase. The 5′-promoter region of human gene hTERT encoding TERT includes binding sites of various transcription factors regulating expression, and various forms of hTERT transcripts were detected. These results indicate that the expression of telomerase can be regulated by transcriptional mechanisms and/or post-transcriptional mechanisms such as selective splicing.
The present inventors have made many efforts to develop a kit and a method for diagnosing cancer using polymorphic minisatellites and, as a result, found that the minisatellites (MS) of secretory mucin gene MUC2 are inherited through meiosis according to Mendelian genetics, and polymorphic minisatellites MUC2-MS6, MUC2-MS7 and hTERT-VNTR 2-2 are related to the development of tumors such as gastric cancer, colon cancer, rectal cancer and prostate cancer, thereby completing the present invention.